Large, diesel-powered trucks and other vehicles often employ turbo-charged intake air systems. Such systems typically include a heat exchanger between the turbo-charger and the engine so as to reduce the temperature of the incoming air after it has been increased by compression in the turbo-charger. Such heat exchangers are known as charge air coolers and are typically positioned in front a conventional water radiator for the engine. Thus, large diesel trucks often have a cooling assembly in which a charge air cooler is positioned in front of a radiator, which is positioned in front a fan assembly.
The temperature drop between the intake and outlet of a charge air cooler can be between 150.degree. to over 200.degree. F., which makes the thermal stress and the possibility for thermal fatiguing of such heat exchangers extreme. A nominal design life for a charge air cooler is about 300,000 vehicle miles and, in order to withstand this stress and achieve such a design life, charge air coolers typically are formed as brazed assemblies of aluminum core tubes and fins that are attached by welding to cast aluminum manifolds. The problem of leakage in a charge air cooler also is greater than in a standard copper/brass water radiator because it is harder to reliably contain air under pressure than water.
As the temperature in which the truck is traveling drops, however, both the charge air cooler and conventional radiator for a truck tend to dissipate too much heat, which interferes with engine efficiency and comfort of the truck driver in the cab. One way of mitigating this problem which is in wide-spread use is to mount a mask or partial shield, usually referred to as a "winter front", in front of the cooling assembly. Typical of truck winter front assemblies is the winter front disclosed in U.S. Pat. No. 4,523,657 to Kooyumjian. The Kooyumjian winter front includes sheet-like panel members which are mounted to the front of the radiator to define a central diamond opening having an area less than the radiator. In the Kooyumjian winter front, the panel flap members can be selectively buttoned by snaps so as to enable variation of the size of the opening in accordance with the weather conditions being experienced by the truck. Smaller openings are used for cold weather so as to limit the area of the core tubes of the radiator which are exposed to direct air flow.
In other prior art charge air coolers, an opening having the shape of a television set or circle is provided that can be selectively reduced in area for colder operating conditions.
Shielding or radiator control assemblies have also been used in connection with automobiles operated under cold conditions. Thus, U.S. Pat. Nos. 1,338,585 1,422,306, 2,155,439, 2,729,202, 3,095,147 and 4,883,139 are typical of systems which have been employed on automobiles to a limited degree. Most of these systems, and particularly the ones involving moveable shutter assemblies, are somewhat complex and costly to install and are not easily removed.
While winter fronts are effective in controlling excess cooling, two problems have been encountered in connection with use of the same. First, in trucks having charge air coolers, winter fronts, such as disclosed in the Kooyumjian patent or the TV set-opening winter fronts, tend to thermally stress the charge air coolers and produce fatigue failures. In the Kooyumjian winter front, for example, there are three opening sizes possible. In all three openings, however, there are core tubes which are not exposed to incoming air. The result is that some of the core tubes are exposed to incoming air, while other core tubes are not exposed to direct air flow. This causes the core tubes to experience substantial temperature differentials, which in turn stresses the core tubes to a substantial degree. Fatigue studies of charge air cooler failures dramatically reveal that core tube failures are significantly higher in the areas which are completely blocked by the winter front.
A second important problem which can incur in connection with winter fronts is that blocking the axially aligned cooling system with a winter front produces mechanical stress on the cooling system fan. As the fan moves across the winter front opening, it "sees" or encounters a stream of incoming air. When the fan moves behind an area which is blocked by the winter front, the loading of the fan is increased. Thus, winter front openings which are asymmetric with respect to the cooling system fan will cause fan assembly mechanical fatigue.
Accordingly, it is an object of the present invention to provide a winter front assembly suitable for use with a charge air cooled vehicle that is effective in controlling cooling system performance without inducing thermal fatigue in the charge air cooler or mechanical stress in the cooling system fan assembly.
The winter front assembly and method of the present invention have other objects and features of advantage which will become apparent from and are set forth in more detail in the accompanying drawing and following the best mode of carrying out the invention.